You are correct in that "torn between" is fine.
I would not use "hence" - it's usually considered a rather pretentious word. I actually used it the other day and my brother-in-law (good naturedly) teased me about it.
Everything you wrote after "I am torn between the red and [the] blue one" is redundant - it's exactly what "torn between" means.
I would use the article "the" before your second choice - it makes it clear that it's "the red one" and "the blue one" not "the red-and-blue one" and then you're wondering what the other choic is.
I'm torn between the red one and the blue one. I love them both!